A flame retardant is an important processing aid for the synthesis of polymer materials, and its demand is second only to plasticizers. Since halogen-based flame retardants easily generate toxic gas (for example, dioxin or furan) during a combustion process, use of the halogen-based flame retardants is currently forbidden by the European Union. Although nitrogen-based flame retardants (for example, melamine or cyanuric acid) and inorganic flame retardants such as aluminum hydroxide or magnesium hydroxide possess environmental characteristics, only the addition of a great quantity thereof can make the prepared material achieve a flame retarding effect. However, a heavy addition of inorganic flame retardants will decrease the mechanical characteristics of the prepared material itself and limit its use. In conclusion, although the flame retarding effect of phosphorus-based flame retardants is not as good as that of halogen-based flame retardants, the phosphorus-based flame retardants are safer than the halogen-based flame retardants and a heavy addition of the phosphorus-based flame retardants is not required, therefore, it is more in line with the current demand for a flame retardant with the characteristics of high efficiency, low smoke, low toxicity, and low addition amount.
Traditionally, there are two ways to adopt flame retardants to improve the flame retarding characteristic of the prepared material. One way is to directly add traditional flame retardants (for example, tricresyl phosphate, tetrabromobisphenol A, antimony trioxide, aluminum hydroxide, and red phosphorus, etc.) to mix with materials, and the advantage thereof is a lower cost and simple production process. However, the flame retarding effect is poor. The compatibility of the traditional flame retardants with resin and whether a heavy addition thereof affects the mechanical characteristics of the prepared material must be considered. The other way is to directly conduct the molecule with flame retarding properties into the resin, and the advantage thereof is to achieve a superior flame retarding effect. However, the cost of the modifier is generally high. Lastly, considering these factors comprehensively, the current trend is still to directly add flame retardants as the mainstream practice.
However, in consideration of a high-temperature manufacturing process of partial high-end products (for example, nylon or polyester composites) and use in a high-temperature environment (for example, aviation, car or electronic products), the heat resistance characteristics of flame retardants is a key factor for consideration. At the present stage, since the heat resistance characteristics of most phosphorus-based flame retardants are poor, available flame retardant of the above-mentioned material is rare, in addition, since most phosphorus-based flame retardants also have the disadvantage of a high water absorption rate, which often causes problems such as increasing the water absorption rate and decreasing the physical property and size stability of the prepared materials when adding the phosphorus-based flame retardants to materials. Therefore, the category of high-temperature and low-water-absorption phosphorus-based flame retardants is rare and expensive which dramatically increases the cost thereof. Although inorganic flame retardants (for example, aluminum hydroxide, magnesium hydroxide, etc.) are cheap, a heavy addition thereof is needed to achieve the desired effect, which tremendously affects the mechanical characteristics of the prepared material and also has the problem of increasing the water absorption rate thereof.